1. Field of the Invention
The present invention generally relates to an ElectroPhoretic Display (EPD), and more particularly, to a method and apparatus for driving an EPD to continuously display data.
2. Description of the Related Art
Recently, the concept of electronic paper has been introduced as a new display device which provides the advantages of a conventional display device and printed paper. Electronic paper is a kind of reflective display which offers the benefits of high resolution, a wide viewing angle, and a bright white background, similar to conventional paper and ink. Among display media, electronic paper has the most excellent visual characteristics and allows for implementation on any substrate of plastic, metal, paper, etc. Even when power is off, an image is maintained on the electronic paper. Due to the absence of a required backlight power supply in electronic paper, the battery lifetime of a mobile terminal is long, thus reducing cost and making it possible to realize a lightweight display. Like conventional paper, electronic paper can be realized over a wide area above all other displays. In addition, electronic paper has a memory function that maintains a displayed image despite a power-off condition.
Electronic paper can be implemented into an EPD. The EPD displays data in black or white according to voltages applied to both ends thereof. The EPD is configured by electrophoresis and microcapsules. A typical cell structure of the EPD is illustrated in FIG. 1. FIG. 1 is a sectional view illustrating the operational principle of the EPD. Referring to FIG. 1, the EPD is configured by forming transparent microcapsules each having black particles 40 and white particles 30 in a colored fluid, mixing the microcapsules with a binder 50, and positioning the mixture between upper and lower transparent electrodes 20 on a substrate 10. When a positive voltage is applied, negatively charged ink particles moves toward a surface, thus displaying the color of the particles. When a negative voltage is applied, the ink particles move downward, thus displaying the color of the fluid. In this manner, text or an image is displayed.
The EPD depends on the electrostatic migration of particles floating in a transparent suspending fluid. When a positive voltage is applied to the EPD, positively charged white particles 30 electrostatically moves toward electrodes near a viewer. The white particles 30 reflect light. On the contrary, if a negative voltage is applied to the EPD, the white particles 30 recede from the viewer and move to electrodes remote from the viewer and the black particles move to the top of the microcapsules, absorbing light. Hence, black is observed. Once particles move to certain electrodes, they are positioned at the same positions even if a voltage is eliminated after the movement. Thus, a bistable memory device can be achieved. Meanwhile, there are also electrophoretic capsules using a single type of particle. Specifically, white charged particles float in a fluid dyed with a dark color within a transparent polymer capsule.
The EPD having the foregoing configuration is a reflective display that makes a viewer comfortable as if he viewed contents printed on paper and has excellent visibility even in daylight. Owing to use of a bistable material, power is consumed only during changing displayed contents, thus making low-power operation possible. Accordingly, the EPD is widely used in displaying static contents, such as a large e-book or a signboard. Further, the EPD can be easily implemented on a curved plane as well as a flat plane due to the elasticity of the material. Therefore, the EPD has a potential for a wide range of applications.
However, since the EPD displays text or an image based on physical movements of colored particles, it has a low switching speed. As a result, the EPD has limitations in dynamic graphic representation. For example, the EPD is not effective in sophisticated dynamic representations such as changing the gray scale of each graphic so that the graphic gets dark gradually, while displaying a plurality of graphics successively at predetermined time intervals.
In contrast, a Liquid Crystal Display (LCD) has a fast response time and thus provides a natural dynamic graphic representation. Nonetheless, the LCD consumes much power and is difficult to be implemented on a curved plane.